The present invention relates to vacuum circuit interrupters, and more particularly to an improved end closure and end seal shield member which is a unitary member. This unitary member implies fabrication by minimizing the number of vacuum seals which need to be made.
The vacuum circuit interrupter has gained wide acceptance as a reliable switching means in electrical transmission and distribution systems over a wide range of operating voltages and currents. A generalized description of vacuum circuit interrupters and a method of fabrication are set out in U.S. Pat. No. 3,656,225. The interrupter structure discussed in this above prior art employs a generally cylindrical ceramic envelope body with metallized end seal surfaces. Each end of the ceramic body has sealed thereto an end closure plate, which is part of a manufacturing subassembly which includes a conductive support rod sealed through the end plate, and a cylindrical end shield member extending from the end plate. An end seal member is sealed to and extends from the perimeter of the end plate to permit final sealing of the evacuated device. Thus, a multiplicity of seals and parts are associated with the envelope end closure. It is desirable to minimize the number and area of vacuum seals to insure reliable long-lived circuit interrupter operation. During circuit interruption, arcing between the separated contacts evolves significant hot materials which can damage the vacuum seals. The interrupter device operating mechanism imparts significant forces to the end closures during contact opening and closing which also stresses the vacuum seal areas.
The use of end shields have been shown to improve the breakdown voltage characteristic for the interrupter. The end shield alters the electric field and electron emission proximate the insulator and metal end seal interface. This insures that voltage breakdown will in general occur across the primary arcing contacts rather than along the insulator body of the interrupter.
The present invention also finds use in a vacuum electrical fuse switching device. The end structure performs the function of being a simplified end seal member while performing a shielding function.